1. Field of the Invention
The present invention relates to an improved telecamera with a high frame frequency, particularly suitable for use, both on its own and together with other telecameras of the same type, in movement analysis systems.
Movement analysis systems are understood here as meaning mainly those systems which analyze the movement of the human body for medical and treatment purposes (diagnosis and rehabilitation of illnesses and traumas affecting the mobility of the body), for study (in science and sport) and also for artistic purposes (study and reproduction of the human movement in animated films and the like). The telecamera forming the subject of the present invention may however be used equally well in the study of other types of movement, both of animals and objects, analysis of which requires a high number of shots per time unit in order to be able to define with precision the nature of the movement itself.
2. Description of the Prior Art
The current movement analysis systems are based on the processing of video signals generated by one or more fixed black-and-white telecameras which record the movement of the subject, or rather the movement of some of the key points of the latter which are highlighted by special markers fixed to the subject; in the case of a human subject, these markers are applied for example to the points, the head and any other point which may used to represent in a significant manner the entire movement of the subject. Typically these markers consist of infrared radiation reflectors; the subject is in fact fully exposed to a source of infrared radiation, such that the infrared radiation reflected by the markers placed on the subject may be more easily detected with respect to the visible-range radiation forming the background image.
The signals emitted by the telecameras thus undergo a first processing operation which consists in extracting the useful information (supplied by the markers applied to the subject) from the background consisting of the visible image of the subject. This processing operation may be performed for example by means of a digital filter able to detect the presence of the markers which appear in the image by means of a light-threshold system, or rather, by means of analysis of the form and the dimension of the marker itself performed for example by means of correlation with a predefined mask. This analysis produces all of the markers' coordinates. Often this stage is preceded by an optical device (filter or separator prism) useful for attenuating the intensity of the visible radiation with respect to the infrared radiation emitted by the markers.
The raw data emitted by the digital filter (including, that is, the coordinates of the individual markers with the passing of time) is then further processed in a processor so as to reconstruct in a virtual and schematic manner the movement of the subject and allow a complete analysis thereof on a rational basis.
The overall processing capacity of the movement analysis systems currently in use is limited by the operating features of their essential components described above, and in particular by:
a) the power of resolution of the telecameras, or rather their sensitive element. This consists of a sensor of the CCD-type (Charge Coupled Device), and its resolution capacity depends on the pixel density (normally expressed as the number of pixels per unit length, in the horizontal and vertical directions); PA1 b) frame repetition rate (referred to above and below simply as "frame frequency"); this parameter represents the frequency of sampling of the movements being analyzed and hence the quantity of information available per unit of time; in a system equipped with a given optical sensor, said parameter indicates the capacity of the latter to perform an accurate description, in analytical terms, of a movement, especially in the case of fast movements; PA1 c) the processing speed of the digital filter; this speed must be fairly high so as to allow filtering of an entire frame before the next frame becomes available, so as to avoid the accumulation of information upstream of the filter and the consequent drawbacks; PA1 d) the processing power of the processor which handles the data output by the filter.
According to the present state of the art and the electronic components market, the most limiting factors among those listed above are those indicated in paras. a) and b) and in particular the latter of the two. While, in fact, there is no difficulty in finding on the market, at an acceptable cost, the components necessary for manufacturing digital filters and processors of adequate power for the aforementioned requirements, there are instead problems in the CCD sector where it is currently not possible to find, in normal mass production, devices which allow both a high image quality and resolution and a high frame frequency.
The technological development of CCD-type sensors is in fact associated mainly with the market of mass-consumption goods (production of videocameras and security systems) and partly with that of filming devices for professional use. The products in the first sector are designed essentially on the basis of low-cost criteria and are therefore characterized by poor or exclusively specialized performance features and for these reasons cannot be conveniently used in the movement analysis systems of the present invention. The products in the second sector, in return for a higher cost, offer both high resolution (thus making it possible to fulfil in a satisfactory manner the requirements mentioned in the aforementioned para. a)) and good versatility of use, but they all have characteristics corresponding to the currently applicable television standards and in particular their frame frequency is still 50 or 60 frames per second.
With the advances made by technology, in the field of the movement analysis systems dealt with by the present invention, it has been established however that this movement detection frequency, although entirely acceptable in a normal television recording which is undoubtedly of high quality, is nevertheless insufficient when one wishes to obtain a significant analytical representation of a fast movement. It has in fact been determined that for a correct representation of these movements a frame frequency of not less than 200 Hz would be necessary.
The most advanced telecameras which have been developed in the technical sector hitherto for the aforementioned applications, however, reach a maximum frequency of 100 Hz. This frequency has been obtained--at the cost of a certain deterioration in the electrical and optical characteristics of the CCD--by modifying the timing circuit of a standard professional 50 Hz CCD, so as to double the response frequency thereof. This "forcing" of the CCD, however, cannot be applied any further without compromising excessively the response quality of the CCD, nor on the other hand can the construction of special high-frequency CCDs be contemplated--even though theoretically possible--since their cost would be such that it would be absolutely impossible to use them for this type of application.